1. Field of the Invention
The present invention relates to a variable magnification copy machine in which a scanning velocity of a scanning means can be varied corresponding to a
2. Description of the Prior Art
In a variable magnification copy machine, the copying magnification can be varied by changing the scanning velocity for a document to be copied. Due to this, the reciprocal travel time of a document scanner means in the enlargement mode takes longer than that in the equal magnification mode in general. Especially, in a conventional copy machine wherein the document platen is moved to scan a document by a driving device including a few one-way clutches, it is impossible to make the document platen return in the direction of the scan since the document platen is driven by a so-called chain-delivery mechanism. In other words, it is impossible to make the platen return from a position corresponding to a top end of a document.
Further, in such a conventional variable magnification copy machine as mentioned above, there are provided a plurality of one-way clutches the number of which is equal to the number of selectable magnifications and, therefore, the running velocity of the chain is varied by switching these clutches. However, since it is hardly possible to change the running velocity of the chain mid way, the scanning velocity of a document upon an exposure and the returning velocity of the document platen become equal as far as one chain-delivery mechanism is installed therein.
Accordingly, when the enlargement mode is selected, both of moving times for going and returning become longer than those in the equal magnification mode and, therefore, the total moving time becomes considerably long.
On the contrary to the above, processes to be employed in a copy machine are so designed, in order to obtain a high speed copy machine, that a stop time of the platen at the starting position thereof can be shortened as short as possible during a multi-copy mode when it is transferred from one copying cycle to the next copying cycle. However, it becomes very difficult to optimize processes corresponding to an individual mode in the case that the moving time of the platen is varied according to the mode selected as mentioned above. In order to avoid these difficulties, processes are so optimized as to meet with the enlargement mode in a conventional variable magnification copy machine wherein a plurality of one-way clutches are used and, accordingly, the waiting time of the platen for adjusting timings is needed and it is determined relatively long when the equal magnification mode or the reduction mode is selected in which the moving time of the platen is relatively short. Namely, the copying cycle can not be speeded up since the waiting time (stop time) of the platen is needed for adjusting timings in the equal magnification mode or the reduction mode.